Apparatus for pyrolytic conversion of hydrocarbons



Feb 141, 1956 K WATSON APPARATUS FOR PYROLYTIC CONVERSION OF HYDROCARBONS Filed June 27, 1947 INERT SEALING GAS LOUVERS I 1. S G 5 5m ST- T N A C 2 R C M G EU EU EU PU VD V V E i Hm Hm Mw CP P OP SM F JNVENTOR. KENNETH MERLE WATSON ATTORNEYS Patented Feb. 14, 1950 APPARATUS FOR PYROLYTIC CONVERSION OF HYDROCARBONS Kenneth Merle Watson, Madison, Wis., assignor to Sinclair Refining Co a corporation of Maine mpany, New York, N. Y.,

Application June 27, 1947, .Serial No. 757,648

1 Claim. (01. .23288) This invention relates to the pyrolytic conversion of hydrocarbons and provides an improved apparatus especially adapted to the carrying out of such pyrolytic conversion processes involving the use of a solid catalyst.

In such operations, a carbonaceous deposit is formed on the solid catalyst during the hydrocarbon conversion and the catalyst must be periodically regenerated to restore its catalytic effectiveness.

In one method of operation previously proposed, the hydrocarbons to be converted are passed continuously upwardly through a downwardly gravitating bed of catalyst, in granular or pelleted form, in a vertically elongated conversion chamber of large transverse dimensions, the catalyst being continuously withdrawn from the lower end of the chamber, regenerated, and returned to the upper end of the chamber. The regeneration is eifected by burning off the carbonaceous deposit by passing the hot catalyst downwardly through a similar vertically elongated chamber countercurrent to a stream of air.

Such operations have entailed expensive and troublesome mechanical elevator means for conveying the catalyst from the lower end of the conversion chamber to the top of the regenerating chamber and again from the lower end of the regenerating chamber to the top of the conversion chamber. Difllculties have also been experienced in effecting uniform contact between the hydrocarbon vapors and the catalyst by reason of the tendency of the vapors to channel upwardly through the bed of catalyst. Similar difficulties have been experienced in the regeneration of the catalyst. The present invention provides an improved apparatus whereby these difiiculties are avoided.

I have described and claimed in my copending applications Ser. Nos. 757,639 and 757,646, each filed June 27, 1947, an improved process and apparatus respectively, in which the catalyst, at an elevated temperature, is caused to gravitate as a continuous vertically elongated bed or column downwardly through a vertically elongated cham her having at least one relatively narrow horizontal dimension. The catalyst is passed from the bottom of the column into a stream of hydro-,

carbon vapors to be processed and is caught up by the vapors and carried in suspension upwardly into an enlarged chamber positioned at an ele vation higher than the upper end of the vertically elongated catalyst bed and in which the catalyst drops out of suspension and flows therefrom by gravity onto the upper end of the catalyst bed.

The hydrocarbon vapors separated from the catalyst pass from the enlarged chamber and are repeatedly passed back and forth through the upper portion of the hot catalyst bed at progres sively different elevations, whereby conversion of the hydrocarbons is effected with the resultant deposit of carbonaceous material on the catalyst. Air, or other oxidizing gas, is similarly passed back and forth through the lower portion of the hot catalyst bed, with a resultant burning off from the catalyst of the carbonaceous deposit formed thereon by the hydrocarbon conversion in the upper portion of the column. The regenerated catalyst is withdrawn from the lower por-' tion of the chamber, suspended in hydrocarbon vapors and returned to the upper end of the catalyst bed, as just described.

In my copending applications, Ser. Nos. 757,640

and 757,647, each filed June 27, 1947, I have described and claimed an advantageous modification of the said process and apparatus in which the catalyst is only partially regenerated in the lower portion of the vertically elongated column and is passed therefrom to a separate regenerat ing chamber in which residual carbon is burned from the catalyst and from which the regenerated catalyst flows into a stream of hydrocar bon vapors to be processed and is carried thereby in suspension into an enlarged chamber positioned at an elevation higher than the upper end of the vertically elongated catalyst bed, as just described.

"The apparatus of my present invention is especially adapted to the carrying out of a process described and claimed in United States Patent No. ,448,334, issued August 31, 1948, on my copending application Ser, No. 757,641, filed concurrently herewith according to which the catalyst is partially regenerated in the lower zone of the vertically elongated body of catalyst and the regeneration is completed and the fully re-,

generated catalyst returned to the upper end of the catalyst body by suspending the partially regenerated catalyst in a stream of additional air flowing upwardly through a second vertically elongated chamber, advantageously in heat exchange relation with the partial regeneration and reaction zones. The hot, fully regenerated catalyst is separated from the suspension in an enlarged chamber positioned above the upper end of the vertically elongated catalyst bed, as just described, and the flue gases pass out from the enlarged chamber carrying therewith in suspension catalyst'fines formed by attrition of the SYS? catalyst in its repeated cycling through the tem.

The present invention thus provides improved means of removing catalyst fines and of conserving the maximum amount of heat for useful purposes.

out in heat exchange relation with the reaction It also results in the conservation of. theamount of air required and provides means whereby the secondary regeneration is carried 3 conditions in the reaction zone by minimizing the temperature gradient. Further, the invention provides greater simplicity of operation and greater simplicity and compactness of apparatus.

Heat for effecting the conversion is supplied in large measure by the burning of the carbonaceous deposit. Additional heat may be supplied where required by preheating the hydrocarbon charge oil vapors.

The hydrocarbon vapors to be converted may be passed through the catalyst bed at progressively higher or progressively lower levels, that is, in a generally countercurrent, or generally concurrent, direction with respect to the direction of catalyst flow. Similarly, air for the partial regeneration of. the catalystmay be passed through the lower portion of the catalyst bed at progressively higher, or progressively lower levels. Due precaution should be taken, however, tominimize intermixing of the gases and vapors.

According to a method of operation specifically described in my said Patent No. 2,448,334, the hydrocarbon vapors are repeatedly passed through the column of catalyst at progressively lower levels in the upper portion of the catalyst bed and the primary regenerating air is passed through the catalyst at progressively higher levels in the lower portion of the catalyst bed. By'this' procedure, a zone of lower pressure is created at the intermediate portion of the bed, both with respect to the conversion section and the partial regenerating section, and the tendency for the gases and vapors to become intermixed is minimized. It is also particularly advantageous to inject an inert sealing or stripping gas into the zone intermediate the conversion and partial regeneration sections. This serves, further, to prevent mixing of combustion gases and hydrocarbon vapors and also serves as a stripping medium for stripping from the spent catalyst readily vaporizable hydrocarbons.

A large amount of heat is liberated in the burning of the carbonaceous deposit and care should be exercised to avoid overheating of the catalyst.

It is usually advantageous to provide means for extracting heat from the bed of catalyst undergoing regeneration in an amount suflicient to avoid excess temperatures. For this purpose, cooling coils may, with advantage, beprovided in the primary regenerating zone adapted to the circulation of water, or other cooling fluid therethrough.

Further catalyst fines are frequently formed by attrition of the catalyst during repeated circulation through the system and it is usually desirable to remove these fines to avoid their excessive accumulation. In the operation of my present apparatus, the catalyst fines are carried off in suspension in the flue gases from the secondary regeneration.

By proper control of the rate of downward flow of the catalyst bed and coordinating therewith.

the rate of flow and number of passes of the hydrocarbon vapors and primary regenerating air therethrough, the catalyst will be substantially spent and ready for regeneration by the time it reaches the lower end of the reaction zone and will be largely regenerated upon reaching the lower end of theprimary regenerating zone.

The optimum rate of downward flow of the catalyst bed will depend primarily upon the typeof catalyst employed, the type of hydrocarbon being converted, operating temperatures, the rate of hydrocarbon feed, the extent of the required reaction, the depth of cracking, for instance, the

number of passes through the catalyst and the thickness of the catalyst bed. The optimum rate of catalyst flow for any particular operation is readily determinable by simple test and is, with advantage, controlled by regulation of the flow of catalyst from the lower end of the primary regenerating zone by means of a suitable valve arrangement.

The apparatus is applicable to various types of hydrocarbon conversion and is adapted to the use of various solid catalyst in granular or pelleted form.

The invention will be more particularly described and illustrated with reference to the accompanying drawing of which:

Figure l is a vertical sectional and somewhat fragmentary view of the apparatus, indicatin intervening sections of similar design; and

Figure 2 is a transverse section along the line 22 of Figure 1.

The part indicated by the reference numeral I is a cylindrical casing advantageously of sheet metal, and closed at its upper end. Coaxially positioned in casing I are cylindrical casings 2, 3, and 4 of progressively smaller diameters which, together with the outer casing form annular chambers 5, 6, and 'I and an interior cylindrical chamber 8. The intermediate annulus 6 and the interior chamber 8 are substantially unobstructed for their entire height. The outer annulus 5 is completely obstructed by a plurality of vertically spaced partitions or spacers 9 of considerable depth, forming a plurality of vertically spaced chambers Ill. The inner annulus I is similarly divided into a plurality of vertically spaced chambers I I by similar partitions or spacers I2.

Each of the chambers I0 and II communicate with the annulus 6 through louvers, the slats of which project upwardly and outwardly from the annulus. 6 into the respective chambers.

Thecasings 2', 3, and 4 terminate short of the upper end of the cylinder formed by casing I so as to form an enlarged cylindrical chamber l3 in the upper part of the apparatus. The uppermost of chambers I0 is closed at its upper end by'a partition 9a, similar to spacers 9. The annulus 6 is in open communication at its upper end withthe lower portion of chamber I3. The upper end of the uppermost chamber I I is closed by means of the partition I2. The upper end of the inner chamber'8 is shown as flaring outwardly and is in open communication with enlarged chamber I3.

The outer casing l' projects'downwardly below the lower ends of the other casing and terminates in hopper I4. The lower ends of the annular chamber 6 open into hopper I4 through an annular connection I5. The walls of the chamber 8 are projected downwardly toward the bottom hopper I4, the chamber 8 opening into the hopper at I6 and the lower end thereof is so shaped and is so positioned with respect to the bottom of hopper I4 as to form a restricted annular passage I'I between the lower end of the wall of chamber 8 and the bottom of the hopper I4.

The lower end of. annulus 6 is interiorly provided with a plurality of horizontally extending distributing plates I8, these plates being perforated in staggered relationship so as to retard the downward flow of catalyst therethrough, as understood in the art. Only two such plates are shown in the drawing but it will be understood that a greater number may be used in accordance-with conventional practice.

The spacers or partitions 9 and I2 are, with advantage, positioned somewhat as shown in the drawing, so as toform chambers I0 and II in staggered positions such that the lower end of a given chamber III is directly opposite the upper end of the next lower chamber II and the lower end of said chamber I I is directly opposite the upper end of the next lower chamber I0. An exception to this arrangement are the stripping zones presently to be described.

The spacers 9, 9a and I2 are, for clarity, shown in the drawing as solid sections, but it will be understood that they may be either solid or hollow. Further, for reduction in weight and material used in fabrication, the respective casings I and 4 may be discontinuous at the points of the respective spacers.

In operation, the annulus 6 is filled with granular catalyst, for instance, by charging the catalyst into the upper enlarged zone I3 through valved conduits I9. Vaporized hydrocarbon oil to be processed is charged through lines into an upper chamber Iii and, from thence, the vapors pass by way of the louvers through the body of catalyst in annulus 6 and into the upper end of the uppermost chamber II. From the lower portion of said chamber I I, the vapors pass back through the body of catalyst into the next lower chamber I0 and so back and forth through the body of catalyst at progressively lower elevations until the vapors reach an intermediate zone ID from which they are withdrawn through one of the valve lines 2I to fractionating apparatus, not shown.

In the drawing a plurality of conversion product draw-off lines 2I are shown leading from progressively lower chambers II]. This is advantageous as it permits withdrawal of conversion products at selective levels from the reaction zone thereby varying the space velocities of the operation and also varying the depth of the intermediate sealing and stripping zone, subsequently described.

The catalyst, which has been substantially spent, continues downwardly through annulus 6 and is stripped of readily vaporizable hydrocarbons remaining thereon by stripping gas, or vapor, steam for instance, introduced into a still lower chamber ID through lines 22.

Air is passed into the lowermost chamber I0 through lines 23, passes therefrom through the louvers, through the bed of catalyst, into the lowermost chamber II and back through the catalyst, into the next higher chamber I0 and so back and forth through the catalyst at progressively higher levels until it reaches an intermediate chamber Itl, below that into which the stripping medium is injected, and the flue gases pass therefrom through conduits 24 to a stack, not shown in the drawing.

The air passing in contact with the hot catalyst results in the burning-therefrom of the major portion of the carbonaceous deposit formed on the catalyst during the hydrocarbon conversion. I Excess heat may be extracted from the catalyst undergoing regeneration by means of cooling coils 25, extending through the bed of catalyst in annulus 6 and through which a cooling medium is circulated. For instance, watermay be circulated through the cooling coils and thereby converted into steam. Any number of cooling coils required may be used to extract from the catalyst an amount of heat necessary to prevent excessive temperatures.

. partially. regenerated catalyst passes from the lower end of the regenerating zone through perforations in the series of plates I8, so positioned as to permit the flow of catalyst therefrom at a retarded rate, dependent upon the angle of repose of the catalyst as previously noted and as understood by the art. From thence, the catalyst flows through the annular connection at the lower end of annulus 6, past the valve 26, and falls into hopper I4.

Air for burning the residual carbon from the catalyst is injected into hopper I5 through lines 21 and passes at relatively high velocity through the restricted annular passage I1 where it picks up the partially regenerated catalyst and carries it in suspension upwardly through the opening I6 and the elongated chamber 8.

In passing upwardly through chamber 8, residual carbon is burned from the catalyst by contact, at high temperature, with the air and the regenerated catalyst is carried upwardly into enlarged chamber I3 where, by reason of decreased velocity of the gaseous suspension, the catalyst drops out of the flue gases and forms a bed of catalyst in the enlarged chamber from which the catalyst flows by gravity onto the elongated body of catalyst in annulus 6, maintaining the annulus completely filled with catalyst.

The flue gases pass from the enlarged chamber through conduit 28 to a precipitator, or stack, not shown and carries therewith in suspension from the system the catalyst fines. The separation of the catalyst from the flue gases is aided and also wear on the apparatus lessened by replaceable bafile 29 positioned in the enlarged chamber I 3 above the upper end of the chamber 8. The separation and even distribution of the separated catalyst in chamber I3 is, with advantage, further facilitated by the gradual increase in transverse area of the chamber 8 near its upper end.

In the apparatus shown, the secondary regeneration of the catalyst is effected in heat exchange relationship with the gases and vapors in the several chambers II. This is particularly advantageous with respect to the hydrocarbon vapors in the reaction zone where the reaction is endothermic. In an operation of the type described, heat for the reaction is supplied primarily through the hot regenerated catalyst and, as the reaction proceeds, there is a tendency toward a lowering of the reaction temperature. By passing the hot flue gases in heat exchange relation with the hydrocarbon vapors, particularly in generally countercurrent relationship as shown, the temperature gradient in the reaction 'zone is lessened and more active, uniform conversion is effected. The secondary air is, with advantage, supplied to hopper I4 through a multiplicity of tubes 27, so as to give substantially uniform distribution of air passing through the restriction IT. The restriction I I functions somewhat as the throat of a venturi and the rate of passage of air therethrough influences the rate of flow of the catalyst upwardly through the secondary regeneration chamber 8. Other catalyst entraining methods may be employed.

The rate of flow of the catalyst through annulus I5 is controlled by a valve mechanism comprising an annular flat ring member somewhat greater width than annulus I5. This ring 26 is adjustably supported by a plurality of shafts 30, extending downwardly through the wall of the hopper I4 and sealed by suitable glands, indicated on the drawingat M. The length of the shafts 30 may be adjusted by means of turn buckles 32 and, further, the lower end of the shafts is connected by linkages 33 to eccentrics 34. The eccentrics are connected by suitable conventional means,.not shown, so they will operate together to impart an oscillatory movement to ring 26, adjustments in leveling the ring 26 and of its distance from the lower end of annulus l being made by the turn buckles 32 interposed in shafts 30.

In the valve arrangement'shown, the ring 26 will completely shut off the flow of catalyst with-, out requiring mechanical seating of the valve. By raising the ring to a point where its edges intercept the angle of repose of the catalyst flowing from annulus IS, the flow is completely stopped. This method of flow control. is particularly advantageous as it avoids crushing the catalyst. The rate of catalyst flow is determined by the height of the ring and the oscile latory motion maintains uniform flow at all points around the annulus IS.

The extent of the regeneration in the primary regenerating zone is subject to considerable variation and is dependent primarily upon the rate of catalyst flow through the annulus 6, the amount of air used and the number of passes of the air through the catalyst. It will also depend upon the thickness of the annulus 6. The amount of secondary regeneration air should be, at least, sufiicient tov carry the catalyst upwardly in suspension at the desired rate and will depend primarily upon the rate of catalyst circulation, the size and density of the cata-. lyst and the transverse area of the chamber 8. Usually, the velocity of the gases passing up.- wardly through chamber 8 should be within the range of 5 to feet per second, the optimum velocity being dependent in large measure upon other conditions, just noted.

The thickness of the annulus 6 may be varied over a considerable range, the optimum thickness dependent upon the particular operating conditions. Generally, its thickness is, with advantage, about 1 to 2 feet. The depth of the spacers 9 and I2 is, with advantage, considerably greater than the thickness of the bed of catalyst in annulus 6 so as to minimize any tendency of the gases or vapors to pass from one chamber to that immediately above or below it, rather than through the catalyst bed to the opposite chamber.

The vertical spacing between the outer and ini-v ner annular chambers, respectively, is shown in the drawing, in some instances, as only slightly greater than the thickness of annulus 6. It will be understood. that the spacings are, with advantage, of greater relative vertical dimension than shown in the drawing, advantageously being considerably greater than the thickness of the annulus 6, as previously noted.

With the exception of the products of combustion, some by-passing of the gases or vapors from one zone, to the next higher or lower zone does not seriously interfere with the operation. However, mixin jof combustion gases from the regenerating zone with the hydrocarbon vapors should usually be avoided and, for this reason, it is particularly advantageous that the spacing just above the primary regenerating zone be substantially greater than the horizontal path through the catalyst bed.

To avoid contamination of the hydrocarbon vapors w th flue cases, from the secondary re:

generation zone, an inert sealinglgas is, switchedvantage, injected into the uppermost zone I! through conduits 35. The sealin gas passes through the louvers of chamber in into the body of catalyst gravitating downwardly from chamber [3.

This gas should be introduced at such a rate that the pressure in the sealing zone is higher than the pressure in chamber l3 and also higher than the pressure in the zone below into which the. charge oil is introduced. There should be sufficientlength of solid catalyst bed in chamber 6 between the point of introduction of the-sealing gas and chamber 13, and also between the point of introduction of the sealing gas and the point of'introduotion of the charge oil vapors, to permit maintenance of such pressure diiferential without excessive flow of sealing as in either direction.

The apparatus shown in the drawing provides for four passes of' hydrocarbon vapors and four passes of the primary regeneration air through the catalyst bed. Frequently a greater number of passes is desirable and is within the contemplation of my invention. Figure 1 of the drawing is somewhat fragmentary, indicating intervening sections of the apparatus of similar design.

Provision for the injection of sealing or stripping gasbetween the conversion and primary regenerating zones may frequently be omitted, particularly when the amount of air passedthrough the primary regeneratingzone is so controlled that, upon reaching the upperend of the primary regenerating zone, the combustion gases are substantially free from uncombined oxygen. Under such conditions, the hot inert combustion products will serve to strip the spent catalyst anda portion of the combustion gases may be caused to pass upwardly through the stripping zone into theconversion zone-byiinposing a slight back-pressure-on the effluent gases.

The apparatus of-the invention is adapted to the use of various types of catalyst, for instance, natural or synthetic earths, silica gels and the like, orvariousinertcarriers having active catalystdeposited-thereomthe size of the particles of the'catalyst is, with advantagaof a mesh within the range of 25 to 40, though, catalyst of larger. or smaller particle size may be employed. Pelletedcatalyst ascoarse as 4 to 10 mesh may be employed. Usually, powdered; catalyst, such as used in the fluidcatalyst processes, is less desirablebecause-of a tendency of the catalyst particles to be carriedoutgof the catalyst bed along with the gases and vapors, but may be used in conjunction with relatively low gas and vapor velocities through'the catalyst bed. Wheresuch finely divided catalyst" is used, means should'be provided for returning to chamber l3the larger particles thereof carried'ofiwith flue gases;

Operating conditions are generally'subject to considerable variation depending upon the particular catalyst. employed, and the nature and theextent of the desiredreaction. Incracking gas oil, for instance, using a silica-alumina type catalyst, thetemperature in the reaction zone is, with advantage, maintained within the range of 750. to-950'F. and the pressure withinthe range of;from 10to 15 poundsper square inch. In theregenerating zones, a temperature within the range of 900 to 1,150 F. is usually satisfactory.

The temperature in the reaction zone is controlled, in large measure, bythetemperature of the catalyst passing-theretofromthe secondary regenerating zone V and the 4 extenvof preheat of the charge oil. The temperature of the catalyst passing from the primary regeneration is controlled by the extraction of heat therefrom, as previously described, any desired number of cooling coils being used for this purpose. Danger of overheating of the catalyst in the secondary regeneration zone is minimized by the burning of the major portion of the carbonaceous deposit in the primary regenerating zone.

In the use of my present apparatus, the extent of contact between the catalyst and the hydrocarbon vapors being converted and also the catalytic activity of the catalyst by which the hydrocarbon vapors are brought into contact may be maintained extremely uniform. Further, an ex ceptionally uniform and-complete regeneration ofthe catalyst is attained." The apparatus has the advantage of high uniformity of the product, increased catalyst life and catalytic effectiveness, increased economy of operation by reason of the elimination of mechanical elevations and also a closer control of operating conditions.

I claim: Apparatus especially adapted to the conversion of hydrocarbons which comprises an enlarged elevated chamber, a coaxially positioned, vertically elongated, annular chamber extending downwardly therefrom, a plurality of outer, vertically spaced annular chambers encircling the elongated vertical chamber, a plurality of inner, vertically spaced annular chambers encircled by the inner wall of the vertically elongated chamber, the relative positions of the inner and outer vertically spaced chambers being staggered so that the upper portion of an inner chamber is opposite the lower portion of an outer chamber and the lower portion of said inner chamber is opposite the upper portion of the next lower outer chamber, each inner and outer chamber communicating with the vertically elongated annular chamber through louvers in the walls of the latter, the slats of the louvers extending upwardly into the respective vertically spaced chambers, a cooling coil positioned in the lower portion of the vertically elongated chamber, a hopper positioned below the lower end of the vertically elongated chamber, an elongated, coaxially positioned inner chamber connecting the elevated chamber with the hopper, jetting means for injecting air into the lower end of the hopper beneath the lower end of the inner chamber and adapted to entrain catalyst from the hopper and carry it upwardly through the inner chamber into the elevated chamber, conduitconnections to the lower, a higher, and at least two intermediate vertically spaced outer chambers, respectively, and a conduit leading from the upper part of the enlarged elevated chamber.

KENNETH WATSON.

No references cited. 

